The invention relates to oscillators operational in the millimeter wave and microwave range, and more particularly to suppression of flicker (1/f) noise.
Phase noise on signal sources used as transmitters and receiver local oscillators in communication and radar systems can cause a degradation in system sensitivity and selectivity. In a digital communication system, for example, phase noise close to the carrier affects the system bit-error rate. In a Doppler radar system, phase noise on both the transmitter and local oscillator sources set a detection limit on Doppler shifted target returns in the presence of a larger clutter return signal that is close in frequency to the target return. Sources with low phase noise at millimeter wavelengths are of interest to various applications where a significant clutter signal is normally present, "Semi-Active Radar Guidance", A. Ivanov, Microwave Journal, Sept. 1983, pp. 105-120. A basic oscillator or VCO source must generally incorporate a noise reduction technique (e.g. phase locking, filtering) to meet typical system requirements on phase noise close to the carrier.
The present invention provides a unique and simple circuit addition integral to an oscillator or VCO source that functions to suppress the generation of output flicker (1/f) noise, the major contributor to phase noise at frequencies close to the carrier. Although the phase noise suppression method is applicable to a variety of source types (e.g. Gunn, Impatt, FET, Bipolar transistor), the subsequent discussion will describe the circuit technique as applied to a Gunn oscillator. It can be used with active devices other than a Gunn diode wherewith oscillator frequency pushing is a significant controller of 1/f noise in the output spectrum.